KR20210015904A - Image processing device and image processing program - Google Patents

Abstract

In a display in which monochrome pixels and color pixels are displayed at the same time, display with more appropriate brightness values is realized. The saturation value of the target pixel or the saturation value of the target small region including the target pixel and its surrounding pixels is obtained, and the corrected gradation characteristic obtained by correcting the target pixel is a color gradation characteristic based on the saturation value. If the target pixel is corrected to match the synthesized grayscale characteristics by mixing the and monochrome grayscale characteristics at a predetermined mixing ratio, and the saturation value is set to c, and the mixing ratio of the color grayscale characteristics is set to W, c is used as a variable. The value of W is expressed by the relationship W=f(c), and an image processing apparatus satisfying the following conditions is provided.
Condition: If the relationship in which the blending ratio W increases proportionally with respect to the saturation value c is W=g(c), then f(c)>αg(c) is satisfied when the saturation value is greater than or equal to the threshold value. There is a value c and a multiplier α, and α≥1.

Description

Image processing device and image processing program

The present invention relates to an image processing apparatus and an image processing program.

In recent years, in medical diagnosis displays, it is possible to perform comprehensive diagnosis by displaying both monochrome pixels and color pixels. When displaying images on such medical diagnostic displays, when displaying monochrome pixels, it is common to correct the brightness value by the GSDF (Grayscale Standard Display Function) curve specified by DICOM (Digital Imaging and Communications in Medicine) standards. Is being carried out. On the other hand, in the case of displaying color pixels, correction of the brightness value by a γ2.2 curve determined by the sRGB standard is widely used.

1 shows the above-described GSDF curve and γ2.2 curve. The relationship between the gradation value input to the display and the brightness value to be displayed is referred to as "gradation characteristic", and as shown in Fig. 1, the gradation characteristic is different between a monochrome pixel and a color pixel. Thus, image processing techniques have been developed for appropriately correcting gradation characteristics for each pixel of an input image. For example, Patent Document 1 is a technology that combines and synthesizes color gradation characteristics and monochrome gradation characteristics based on a blending ratio determined based on a saturation value in pixels of an input image or a saturation value in an area unit. Is disclosed.

Japanese Unexamined Patent Publication No. 2016-180787

However, in the technique of Patent Document 1, in the case of using a saturation value in units of pixels, a diagnostician such as a doctor who is familiar with diagnosis on a display that performs only color gradation characteristic correction by γ2.2 curve on a color image There is a concern that it is difficult to perform accurate diagnosis because the color image displayed on the display feels dark. In addition, in the case of using the saturation value in units of areas, there is a fear that the screen display collapses depending on the saturation calculation result for each area, and an appropriate brightness value cannot be output.

The present invention has been implemented in view of these circumstances, and an object of the present invention is to provide an image processing apparatus and an image processing program for realizing display with more appropriate brightness values in a display that displays monochrome pixels and color pixels together. .

According to the present invention, an image processing apparatus including a saturation value acquisition unit and a correction unit, wherein the saturation value acquisition unit acquires a saturation value of a target pixel or a saturation value of a target small region including the target pixel and surrounding pixels. And the correcting unit so that the corrected gradation characteristic obtained by correcting the target pixel matches the gradation characteristic synthesized by mixing the color gradation characteristic and the monochrome gradation characteristic at a predetermined mixing ratio based on the saturation value. When is corrected, the saturation value is c, and the blending ratio of the color gradation characteristics is W, the value of W when c is a variable is represented by the relationship W=f(c), and the following conditions A satisfactory image processing apparatus is provided.

Condition: If the relationship in which the blending ratio W increases proportionally with respect to the saturation value c is W=g(c), then f(c)>αg(c) is satisfied when the saturation value is greater than or equal to the threshold value. There is a value c and a multiplier α, and α≥1.

Therefore, it becomes possible to change the relationship between the saturation of the target pixel and the mixing ratio of the color gradation characteristics when the saturation of the target pixel exceeds a predetermined threshold, and suppress the mixing ratio of the color gradation characteristics when the saturation of the target pixel is low. Meanwhile, when the saturation of the target pixel is high, the mixing ratio of the color gradation characteristics can be increased. Therefore, when the saturation of the target pixel is high, it becomes possible to realize correction to increase the brightness value, and display display with a more appropriate brightness value becomes possible. In addition, since the saturation value for each area is not used, there is no fear that the screen display is collapsed due to the difference in the saturation value for each area.

Hereinafter, various embodiments of the present invention will be illustrated. Embodiments shown below can be combined with each other. In addition, each feature independently constitutes the invention.

Preferably, the correction unit includes a mixing unit for determining a mixing ratio of the color gradation characteristics for color pixels and the monochrome gradation characteristics for monochrome pixels based on the obtained saturation value.

Preferably, the relationship f(c) includes a relationship W1=f1(c) below the threshold and a relationship W2=f2(c) above the threshold, and an arbitrary saturation value below the threshold. If c1 and c2 are arbitrary saturation values equal to or greater than the threshold, f1(c1)≦f2(c2) is satisfied.

Preferably, the relationship f1(c) below the threshold is a proportional function.

Preferably, there is a second threshold when the threshold is the first threshold, the second threshold is equal to or greater than the first threshold, and the saturation value is equal to or greater than the second threshold, the relationship f2(c) The slope of decreases toward zero.

Preferably, the relationship f(c) is at least part of the sigmoid function.

Preferably, the correction unit also uses a relationship in which the threshold value is set to be larger as the difference between the brightness value in the color gradation characteristic of the target pixel and the brightness value in the monochrome gradation characteristic of the target pixel is increased. Correction is performed by determining the ratio W.

According to another aspect of the present invention, an acquisition step of acquiring a saturation value of a target pixel or a saturation value of a target small region including the target pixel and surrounding pixels thereof, and the target pixel is corrected by the correction unit. And a correction step of correcting the target pixel so that the obtained gradation characteristic after correction matches the gradation characteristic synthesized by mixing the color gradation characteristic and the monochrome gradation characteristic based on the saturation value at a predetermined mixing ratio, and the saturation When the value is c and the blending ratio of the color gradation characteristics is W, the value of W when c is a variable is represented by the relationship W=f(c), and an image processing method that satisfies the following conditions is Is provided.

Condition: If the relationship in which the blending ratio increases proportionally from the minimum value to the maximum value as the saturation value increases from the minimum value to the maximum value is W=g(c), when the saturation value is greater than or equal to the threshold value, f( There is a saturation value c and a multiplier α for satisfying c)>αg(c), and α≥1.

According to another aspect of the present invention, as an image processing program for causing a computer to function as an image processing apparatus including a saturation value acquisition unit and a correction unit, the saturation value acquisition unit provides the saturation value of the target pixel or the target pixel and the same. An acquisition step of acquiring a saturation value of a target small area including surrounding pixels, and a corrected gradation characteristic obtained by correcting the target pixel are mixed with a color gradation characteristic and a monochrome gradation characteristic based on the saturation value. Comprising the step of correcting the target pixel so as to match the gradation characteristics synthesized by mixing at a ratio, and if the saturation value is c and the blending ratio of the color gradation characteristics is W, W when c is a variable The value of is represented by the relationship W=f(c), and an image processing program that satisfies the following condition is provided.

Condition: If the relationship in which the blending ratio increases proportionally from the minimum value to the maximum value as the saturation value increases from the minimum value to the maximum value is W=g(c), when the saturation value is greater than or equal to the threshold value, f( There is a saturation value c and a multiplier α for satisfying c)>αg(c), and α≥1.

1 is a graph showing a GSDF curve and a γ2.2 curve.
2 is a hardware configuration diagram of the image processing apparatus 100 according to the first embodiment.
3 is a functional block diagram of the control unit 1.
In Fig. 4, Fig. 4A is a diagram showing a look-up table L1 for a monochrome pixel. 4B is a diagram showing a lookup table L2 for color pixels.
5 is a diagram showing a relationship between a saturation value c and a blending ratio W.
6 is a processing flow chart for explaining the procedure of correction processing.
In FIG. 7, FIG. 7A is a diagram showing a relationship between a saturation value and a blending ratio in Modification Example 1. FIG. 7B is a diagram showing a relationship between a saturation value and a blending ratio in Modified Example 2. FIG. 7C is a diagram showing a relationship between a saturation value and a blending ratio in Modified Example 3. FIG.
In Fig. 8, Fig. 8A is a diagram showing the difference between the brightness value between the GSDF curve and the γ2.2 curve. Fig. 8B is a diagram showing the difference ratio of the brightness values between the GSDF curve and the γ2.2 curve.
In Fig. 9, Fig. 9A is a diagram in which regions of input grayscale values are divided for each size of a difference ratio with respect to Fig. 8B. Fig. 9B is a diagram in which a plurality of relations between a saturation value c and a blending ratio W are defined in correspondence with division of an input gray level value.
10 is a processing flow chart for explaining the procedure of the correction processing according to the second embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In particular, "unit" in the present specification may represent a combination of a hardware resource implemented by, for example, a broader circuit and information processing of software that can be specifically realized by the hardware resource.

Further, a circuit in a broad sense is a circuit realized by at least appropriately combining a circuit, circuitry, a processor, and a memory. That is, Application Specific Integrated Circuit (ASIC), programmable logic device (e.g., Simple Programmable Logic Device (SPLD)), Complex Programmable Logic Device (CLPD), and field It includes a programmable gate array (Field Programmable Gate Array: FPGA).

In addition, in the present specification, a single pixel of an input image or an area including the pixel and surrounding pixels of the input image is defined as a small area. In addition, an image is assumed to include both a still image and a moving image, and in the case of a moving image, it is assumed that one frame among them is indicated unless otherwise specified.

Further, in the embodiments described in detail below, various types of information and concepts including these are handled, but these are binary bits consisting of 0 or 1, represented by the high and low signal values, and communicated on a circuit in a broad sense. E operation can be executed. Specifically, "small area", "input grayscale value", "saturation value", "brightness value", and the like may be included in this information/concept. These will be described in detail again as necessary.

<First embodiment>

(1.1. Configuration of the image processing apparatus 100)

The configuration of the image processing apparatus 100 will be described with reference to FIG. 2. On the other hand, in the description using FIG. 2, only the basic function of each component is described, and the detailed description of the process will be described later.

As shown in Fig. 2, the image processing apparatus 100 includes a control unit 1, a storage unit 2, an operation unit 3, a display unit 4, a backlight 5, a communication unit 6, and , With a bus (7). The control unit 1 reads a program (not shown) stored in the storage unit 2 and executes various arithmetic processing, and is configured by, for example, a CPU or the like.

The storage unit 2 stores a look-up table for performing gradation characteristic correction applied to the display unit 4 and various types of data and programs, and is constituted by, for example, a memory, an HDD, or an SSD. Here, the program may be pre-installed at the time of shipment of the image processing device 100, may be downloaded as an application from a site on the Web, or other information processing device or recording medium by wired or wireless communication. It may be transmitted from The lookup table will be described in detail below.

The operation unit 3 operates the image processing apparatus 100 and is constituted by a motion recognition device using, for example, a switch, button, mouse, keyboard, touch panel, voice input unit, camera, or the like. For example, various setting information on the OSD (On Screen Display) is manipulated by the operation unit 3.

The display unit 4 displays input image data (including still images and moving pictures) as an image, and is constituted by, for example, a liquid crystal display, an organic EL display, a touch panel display, electronic paper, or other displays.

The backlight 5 illuminates the display unit 4 from the rear surface of the display unit 4. On the other hand, when the display unit 4 is not a liquid crystal display, the backlight 5 is unnecessary.

The communication unit 6 transmits and receives various data to and from other information processing devices or components, and is configured by arbitrary I/O. The bus 7 is composed of a serial bus, a parallel bus, or the like, and electrically connects each unit to enable transmission and reception of various data.

Each component may be realized by software or by hardware. When realized by software, various functions can be realized by the CPU executing the program. The program may be stored in the built-in storage unit 2 or may be stored in a non-transitory computer-readable recording medium. Further, a program stored in an external storage unit may be read and realized by so-called cloud computing. When implemented by hardware, it can be implemented by various circuits such as ASIC, FPGA or DRP.

(1.2. Function composition)

The function of the control unit 1 will be described with reference to FIG. 3. As shown in FIG. 3, the control unit 1 includes a determination unit 11, a saturation value acquisition unit 12, and a correction unit 20. The correction unit 20 includes a mixing unit 21, a monochrome correction unit 22, and a color correction unit 23.

The determination unit 11 determines whether the target pixel of the input image data input to the image processing apparatus 100 is monochrome or color. Here, various methods are known as the determination method. As an example, if the input gradation values (R, G, B) of the target pixel are plotted in the RGB space, and the distance from the straight line defined in the (1, 1, 1) direction in the RGB space is limited to the reference value, the monochrome You may use the method of judging by. On the other hand, in this embodiment, the input gradation value is defined as a 10-bit digital value taking values from 0 to 1023.

The saturation value acquisition unit 12 acquires a saturation value (hereinafter also referred to as saturation value c) with respect to the target pixel of the input image data input to the image processing apparatus 100 based on the input gradation value. In this embodiment, the saturation value is defined as an 8-bit digital value taking a value of 0 to 255. Here, the saturation value acquisition unit 12 may acquire a saturation value for a target small region including the target pixel and surrounding pixels. In that case, for example, the saturation value of the target small region may be calculated by calculating an additive average with respect to the saturation values corresponding to each of the target pixel and the surrounding pixels, or one saturation value in the target small region is a representative value. You may acquire as.

The correction unit 20 corrects the color gradation characteristics for color pixels and the monochrome gradation characteristics for monochrome pixels with respect to the input image data. Here, the gradation characteristic refers to the relationship between the input gradation value of the target pixel of the input image data and the brightness value when the target pixel is output from the display. Color gradation characteristic correction refers to correcting gradation characteristics for color pixels. The monochrome gradation characteristic correction refers to correcting the gradation characteristic of a monochrome pixel.

The blending unit 21 determines a blending ratio (hereinafter, also referred to as blending ratio W) of the color tone characteristic and the monochrome tone characteristic based on the chroma value acquired by the chroma value acquisition unit 12. Details of the specific processing of the mixing unit 21 will be described in detail below.

The monochrome correction unit 22 performs monochrome gradation characteristic correction for each target pixel of the input image data. Details of the specific processing of the monochrome gradation characteristic correction performed by the monochrome correction unit 22 will be described in detail below.

The color correction unit 23 performs color gradation characteristic correction for each target pixel of the input image data. Details of specific processing of color gradation characteristic correction performed by the color correction unit 23 will be described in detail below.

The storage unit 2 stores, as an example, a look-up table L for performing gradation characteristic correction, and a blending ratio table K in which a relationship between a saturation value c and a blending ratio W is defined.

The display unit 4 is configured to display the input image data with a brightness value corresponding to the gradation characteristic corrected by the monochrome correction unit 22 or the color correction unit 23 with respect to the target pixel of the input image data.

(1.3.Lookup Table)

The lookup table L stored in the storage unit 2 will be described with reference to Figs. 4A and 4B. However, the method of defining the lookup table L is only an example, and is not limited to the mode illustrated here.

4A and 4B, the storage unit 2 stores a look-up table L1 for monochrome pixels and a lookup table L2 for color pixels. In the lookup table L1, input grayscale values from 0 to 1023 and brightness values corresponding thereto are defined. Here, the brightness values M0 to M1023 are values that can be expressed as 0 to 100%, 0% is the lowest brightness that can be expressed by the display unit 4, and 100% is the maximum brightness that can be expressed by the display unit 4 . In the lookup table L1, the input grayscale value and the brightness value are mapped one-to-one to satisfy the GSDF curve determined by the DICOM standard. On the other hand, the brightness value may be defined as a 16-bit digital value taking a value from 0 to 65535 instead of 0 to 100%.

On the other hand, in the lookup table L2, an input grayscale value and a brightness value for each RGB corresponding thereto are defined. In the lookup table L2, the relationship defined by the lookup table L1 is defined for each RGB. That is, the brightness values R0 to R1023 correspond to R (red), the brightness values G0 to G1023 correspond to G (green), and the brightness values B0 to B1023 correspond to B (blue). In the lookup table L2, input gradation values and brightness values are corresponded one-to-one for each RGB so as to satisfy the γ2.2 curve determined by the sRGB standard.

Accordingly, by referring to the lookup table L1 regarding the input grayscale value of the monochrome pixel, the grayscale characteristic correction can be performed so that the brightness value satisfies the GSDF curve. Further, with respect to the input gradation value of the color pixel, by referring to the lookup table L2, gradation characteristic correction can be performed so that the luminance value satisfies the ?2.2 curve.

(1.4. Mixing part (21))

The blending unit 21 is based on the saturation value c acquired by the saturation value acquisition unit 12, the color gradation characteristics for color pixels (equivalent to lookup table L2) and the monochrome gradation characteristics for monochrome pixels (equivalent to lookup table L1). Determine the mixing ratio W for mixing. Here, the blending ratio W means that when W=1, the color gradation characteristic becomes, and when W=0, it becomes the monochrome gradation characteristic. Further, when W=0.5, a gradation characteristic obtained by mixing 50% of a color gradation characteristic and a monochrome gradation characteristic is synthesized.

The relationship between the saturation value c and the blending ratio W is defined in the blending ratio table K stored in the storage unit 2. The mixing unit 21 can determine the mixing ratio W corresponding to the saturation value c acquired by the saturation value acquisition unit 12 by referring to the mixing ratio table K.

5 is a diagram showing a relationship W=f(c) (hereinafter, also referred to as a correspondence relationship f(c)) between the saturation value c and the blending ratio W, and corresponds to the blending ratio table K. In FIG. 5, as the saturation value c increases from the minimum value 0 to the maximum value 255, the blending ratio W increases proportionally from the minimum value 0 to the maximum value 1, W=g(c) (hereinafter also referred to as the proportional relationship g(c). To) is indicated. In addition, the first threshold P and the second threshold Q for the saturation value c are shown.

As shown in Fig. 5, the correspondence relationship f(c) is a value greater than the proportional relationship g(c) in the area where the saturation value c is equal to or greater than the first threshold P (that is, the area after the point X in f(c)). It is structured to take. In other words, when the saturation value c is equal to or greater than the first threshold P, the saturation value c and the multiplier α for satisfying the condition f(c)>αg(c) exist, and α≥1.

With this configuration, compared to the proportional relationship g(c) that increases the blending ratio W of the color tone characteristics in proportion to the increase of the saturation value c, increasing the blending ratio W of the color tone characteristics in the case of the first threshold P or more It becomes possible. As a result, in the case of the first threshold P or more, the ratio of the color gradation characteristic to the input pixel is increased, and an image with a higher brightness value can be realized.

Here, the value of the multiplier α is 1 to 20, preferably 1.5 to 15, and more preferably 2 to 10. The value of the multiplier α is specifically, for example 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5 , 11, 11.5, 12, 12.5, 13, 13.5, 14, 14.5, 15, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, between any two numbers exemplified here It may be within the range of.

Here, when the saturation value c is equal to or greater than the first threshold P, the above condition is satisfied with respect to a saturation value of 50% or more of the saturation values from the first threshold P to the maximum value 255. The ratio is specifically 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, and within the range between any two numbers exemplified herein. May be. More preferably, the ratio may be 70%. In this way, it becomes possible to increase the blending ratio of the color gradation characteristics more than the blending ratio in the case of the proportional relationship g(c) with respect to 70% or more of the saturation value c of the first threshold P or more, and the saturation value c or more of the first threshold P It becomes possible to represent an image with an improved brightness value of 70% or more.

In addition, preferably, when the saturation value c is greater than or equal to the first threshold P, the above condition is satisfied with respect to the saturation value included in a region of 50% or more with a lower value among the saturation values from the first threshold P to the maximum value 255. . The area is specifically 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% with lower values, between any two numbers exemplified herein. It may be within the range of. More preferably, the ratio may be set to 90%. In this way, it becomes possible to increase the blending ratio of the color gradation characteristics in a region of 90% of the saturation values from the first threshold P to the maximum value 255 in the correspondence relationship f(c) with a low value. As a result, it becomes possible to express an image in which the brightness value is improved in a region of 90% or more of which the value is low among the saturation values from the first threshold P to the maximum value 255.

In the example shown in Fig. 5, the relationship f(c) between the saturation value c and the blending ratio W is the relationship W=f1(c) at the first threshold P or less, and the relationship W at the first threshold P or more. =f2(c) is included, and if an arbitrary saturation value equal to or less than the first threshold P is c1, and an arbitrary saturation value equal to or higher than the first threshold P is c2, f1(c1) ≤ f2(c2) is satisfied. .

In addition, in the example of FIG. 5, f1(c) is a proportional function, and is consistent with the proportional relationship g(c). Meanwhile, in the example of FIG. 5, f2(c) is at least a part of a sigmoid function. Here, f1(c) and f2(c) are not limited to this, and may be a relationship satisfying f1(c1)≦f2(c2). In this way, by using f1(c) as a proportional function, it is possible to increase the mixing ratio of the monochrome gradation characteristics in the region where the saturation value c is low. Therefore, in the region where the saturation value c is low, the occurrence of noise due to the high blending ratio of the color gradation characteristics is suppressed, while preventing an increase in the deviation from the intended color display by excessively improving the ratio of the monochrome gradation characteristics. It becomes possible.

In addition, as for f(c), in a region where the saturation value c is equal to or greater than the first threshold P and equal to or less than the second threshold, the slope thereof increases, and the value of the blending ratio W increases significantly. In addition, in the region where the saturation value c is greater than or equal to the second threshold and is less than or equal to the maximum value of 255 (i.e., the region after the point Y in f(c)), the slope decreases toward zero, and f(c) is gentle. Increases.

By defining the relationship between the saturation value c and the blending ratio W in this way, the first threshold value while correcting the gradation characteristics in which the monochrome gradation characteristics and the color gradation characteristics are mixed by suppressing the mixing ratio of the color gradation characteristics in a region with a low saturation value c. In the region of P or more, it becomes possible to increase the mixing ratio of color gradation characteristics.

(1.5. Monochrome correction unit (22))

The monochrome correction unit 22 obtains a brightness value by referring to the lookup table L1 with respect to the input gradation value of the target pixel determined by the determination unit 11 as a monochrome pixel. As described above, the lookup table L1 is specified to satisfy the GSDF curve. As a result, it becomes possible to display a monochrome pixel with a brightness value satisfying the GSDF curve.

Further, the monochrome correction unit 22 determines a brightness value for mixing based on the blending ratio W with reference to the lookup table L1 with respect to the input gradation value of the target pixel determined by the determination unit 11 as a color pixel. .

(1.6. Color correction unit (23))

The color correction unit 23 refers to the lookup table L1 with respect to the input gradation value of the target pixel determined by the determination unit 11 as a color pixel, and determines a brightness value for mixing based on the blending ratio W.

The control unit 1 causes the pixels determined by the determination unit 11 to be monochrome pixels to be displayed on the display unit 4 based on the brightness value determined by the monochrome correction unit 22. On the other hand, the control unit displays a pixel determined by the determination unit 11 as a color pixel on the display unit 4 based on the brightness value determined by the monochrome correction unit 22 and the brightness value determined by the color correction unit 23.

Hereinafter, the brightness value in the case of displaying color pixels will be described in detail. As an example, when the input gradation value of the target pixel is (R, G, B) = (80, 90, 100) and the blending ratio W of the color gradation characteristics is 0.7, the brightness values after mixing (MR, MG, MB) Is calculated by the following (Equation 1) to (Equation 3).

MR=L2(80)Х0.7+L1(80)Х0.3 (Equation 1)

MG=L2(90)Х0.7+L1(90)Х0.3 (Equation 2)

MB=L2(100)Х0.7+L1(100)Х0.3 (Equation 3)

Here, when the input value is 80, the brightness value of the lookup table L1 is set to L1(80), and the brightness value of the lookup table L2 is set to L2(80). The same is true for other input values 90 and 100.

(1.7. Procedure of correction processing)

The procedure of the correction processing in this embodiment will be described with reference to FIG. 6. The following processing is executed by the control unit 1 constituted by a CPU, for example.

In step S10, the determination unit 11 performs a monochrome determination on the target pixel of the input image data. When the determination unit 11 determines the input pixel as monochrome, step S45 is executed. On the other hand, when the determination unit 11 determines the input pixel as a color, step S20 is executed.

In step S20, the saturation value acquisition unit 12 acquires the saturation value c for the target pixel or the target small region determined as color by the determination unit 11.

Next, in step S30, the blending unit 21 determines the blending ratio W of the color gradation characteristics by referring to the blending ratio table K stored in the storage unit 2 based on the acquired chroma value c. .

Subsequently, in step S40, the monochrome correction unit 22 and the color correction unit 23 refer to the lookup tables L1 and L2 based on the input gradation value of the input pixel, and the lookup table L1 based on the blending ratio W determined in step S30. And L2 values are mixed to determine the brightness value after the synthesized gradation correction.

On the other hand, in step S45, the monochrome correction unit 22 refers to the lookup table L1 stored in the storage unit 2 with respect to the target pixel determined to be monochrome by the determination unit 11 to determine the input gradation value of the target pixel. Determine the corresponding brightness value.

In step S50, the correction unit 20 determines whether or not the processing of S10 to S45 has been completed with respect to all pixels of the input image data. If the processing has not been completed, step S10 is executed again. On the other hand, when the processing is completed, step S60 is executed.

In step S60, the control unit 1 controls the display unit 4 to display the input image data at the brightness value determined in step S40 and/or step S45.

As described above, in this embodiment, the control unit 1 includes the saturation value acquisition unit 12 and the correction unit 20. The saturation value acquisition unit 12 acquires a saturation value of a target pixel or a target small region of the input image data. The correcting unit 20 is a gradation synthesized by mixing the color gradation characteristics for color pixels and the monochrome gradation characteristics for monochrome pixels at a predetermined mixing ratio in the corrected gradation characteristics obtained by correcting the target pixel based on the acquired saturation value. Correct the target pixel to match the characteristics.

Here, if the saturation value is c and the blending ratio of the color gradation characteristics is W, the correspondence relationship W=f(c) of the blending ratio W when c is a variable is f with respect to the proportional relationship g(c) (c)> A saturation value c and a multiplier α for satisfying αg(c) exist, and the condition α≥1 is satisfied.

By setting it as the above structure, it becomes possible to improve the blending ratio W of the color gradation characteristics in a region equal to or higher than the first threshold P compared to the case where the proportional relationship g(c) is determined. As a result, the gradation characteristic mixed in the region of the first threshold P or higher can be brought close to the gradation characteristic based on the γ2.2 curve.

(1.8. Modification)

Fig. 7A shows the correspondence relationship f(c) between the saturation value c and the blending ratio W as the first modification. In this example, the correspondence relationship W=f(c) of the blending ratio W to the saturation value c is represented by one sigmoid function. Specifically, the correspondence relationship f(c) is represented by the following equation.

Here, for the coefficients a and b, in the example shown in Fig. 7A, a = 18 and b = 128, but are not limited to this example. By doing so, it becomes possible to define the relationship between the saturation value and the blending ratio so as to satisfy the above-described condition using one function, and it becomes easy to define the correspondence relationship f(c).

Fig. 7B shows a correspondence relationship f(c) between the saturation value c and the blending ratio W as the second modification. In this example, f1(c) is a linear function and f2(c) is a constant in the correspondence relationship W=f(c) of the blending ratio W to the saturation value c. By doing so, it becomes possible to obtain the blending ratio W with respect to the saturation value c with a simpler operation.

Fig. 7C shows the correspondence relationship f(c) between the saturation value c and the blending ratio W as the third modification. In this example, until the saturation value c reaches the threshold value P, the correspondence relationship f(c) <the proportional relationship g(c). Even in this way, it is possible to obtain the same effects as in the above embodiment.

Here, in Fig. 7C, the relationship between the saturation value c and the blending ratio W until reaching the threshold P is not limited to monotonic increase. For example, it may be equal to or less than the threshold P, and the mixing ratio W may be zero. Specifically, as shown by the dashed-dotted line in Fig. 7C, an arbitrary threshold value between 0 and P is S, until 0≤c≤S, W=0, and in c≥S, W is f(P) You may make it monotonically increase toward.

Hereinafter, the reason for increasing the mixing ratio of the monochrome gradation characteristic when the saturation value c is low in the above embodiment will be described. In a low-saturation image in which monochrome pixels and color pixels are mixed, when the difference between the brightness values of the monochrome gradation characteristics for monochrome pixels and the color gradation characteristics for color pixels is large, the difference in the brightness values is perceived by the user as noise. ) In some cases. Therefore, it is necessary to perform gradation characteristic correction in which the mixing ratio of the monochrome gradation characteristic is increased with respect to the low-saturation image color pixels so that noise is not perceived.

Similarly, in a high-saturation image in which a monochrome pixel and a color pixel are mixed, when the difference between the brightness value of the monochrome grayscale characteristic and the color grayscale characteristic is large, there is a concern that the difference in the brightness value is perceived as noise. However, noise is rarely perceived in a high-saturation image. The reason is that the brightness of the color (each RGB color) is lower than that of the monochrome, so it is difficult for the user to perceive the difference in brightness in high saturation.

Another reason is that it is easy to perceive a difference due to color difference in a low-saturation image, but it is difficult to perceive a difference due to color difference in a high-saturation image. In this way, in a high-saturation image, even if the blending ratio of color gradation characteristics is increased, the appearance of noise becomes such that the user does not care. And, in high saturation, by increasing the mixing ratio of the color gradation characteristics, it becomes possible to prevent the color image displayed on the display from feeling dark without lowering the image quality.

<2. 2nd embodiment>

In the second embodiment, in consideration of the difference between the brightness value defined by the GSDF curve with respect to the input gray level value and the brightness value defined by the γ2.2 curve, the correspondence relationship F(c) between the saturation value c and the blending ratio W is considered. ) Is different from the first embodiment. On the other hand, the same reference numerals are assigned to the same configuration as in the first embodiment, and the description is not repeated.

In Fig. 8A, a GSDF curve and a γ2.2 curve are shown. Here, when the input grayscale value is Z, the brightness value on the γ2.2 curve is B1, and the brightness value on the GSDF curve is B2. As shown in Fig. 8A, the difference between the brightness value B1 and the brightness value B2 varies according to the input gray scale value.

In Fig. 8B, the difference ratio C between the brightness value B1 and the brightness value B2 is shown based on Fig. 8A. Here, the difference ratio C is calculated by the following (Equation 4).

C=|(B1-B2)/B2|(|| is an absolute value) (Equation 4)

Here, the difference between the brightness value B1 and the brightness value B2 with respect to the input grayscale value is that the difference between the monochrome grayscale characteristic correction by the GSDF curve and the color grayscale characteristic correction by the γ2.2 curve is large. it means. In this case, if the mixing ratio W of the color gradation characteristics is rapidly increased, noise is generated and image quality is degraded.

Thus, as shown in Fig. 9A, regions I to IV are defined according to the magnitude of the difference ratio between the brightness value B1 and the brightness value B2. In addition, input grayscale values corresponding to areas I to IV are defined as areas (1) to (4).

Further, as shown in Fig. 9B, a plurality of correspondences between the saturation value c and the blending ratio W are prepared as shown in F1(c) to F4(c). Here, in Figs. 8B and 9, the correspondence relationship F1(c) is applied to the input gray scale value belonging to the region (corresponding to the region 1) in which the difference between the brightness value B1 and the brightness value B2 is the smallest. Then, the correspondence relationship F2(c) is applied to the input gradation value in a region (corresponding to the region 2) in which the difference between the brightness value B1 and the brightness value B2 is the next smallest. In this way, the correspondence relations F1(c) to F4(c) used for determining the blending ratio are determined based on the input gradation value.

Here, as the input gradation value when determining the correspondence relationship F1(c) to F4(c), three arithmetic averages of the input gradation values (R, G, B) of the target pixel may be used, or three One specific one of them may be used as a representative value.

The relations F1(c) to F4(c) can be specifically realized by changing the coefficient b in the above-described [Equation 1]. As an example, F1(c) is a=18, b=55, F2(c) is a18, b=70, F3(c) is a=18, b=96, F4(c) is a=18, b It contains the sigmoid function described in [Equation 1] with =128.

And, the first threshold values P1 to P4 respectively corresponding to the relations F1(c) to F4(c), P1 is the smallest, P2 and P3 are slightly larger, and P4 is the largest. In other words, as the difference ratio C between the brightness value B1 and the brightness value B2 increases, the first threshold value is set to increase. Mixing ratio tables K1 to K4 in which correspondence relations F1(c) to F4(c) set in this way are respectively defined are stored in the storage unit 2.

The blending unit 21 determines the blending ratio W by referring to the blending ratio table K corresponding to the input gray scale value of the target pixel. And, similarly to the above-described embodiment, the color correction unit 23 performs grayscale characteristic correction on the input grayscale value by referring to the lookup tables L1 and L2 based on the determined blending ratio W.

With this configuration, in the input grayscale value where the absolute value of the difference between the brightness value determined by the GSDF curve and the brightness value determined by the γ2.2 curve is large, the mixing ratio of the color grayscale characteristics can be suppressed when the saturation is low. I can. In addition, in an input grayscale value having a small difference, the mixing ratio can be increased even when the saturation is low. As a result, it becomes possible to determine an appropriate blending ratio according to the input gradation value.

The procedure of the correction processing in the second embodiment will be described with reference to FIG. 10. On the other hand, the same reference numerals are assigned to the same processing as in the second embodiment, and the description is not repeated.

In step S25 after step S20, the correction unit 20 determines the relationship F(c) to be applied to the target pixel based on the input gray scale value of the target pixel. Then, step S30 is executed to determine the blending ratio W for the target pixel.

<3. Other embodiments>

The application of the present invention is not limited to the above embodiment. For example, after referring to a 3D lookup table defining color gradation characteristics, a so-called 3D-1D lookup table referring to a common 1D lookup table for color and monochrome can also be applied.

In addition, the brightness value satisfying the GSDF curve, the brightness value satisfying the γ2.2 curve, and the blending ratio W based on the saturation value c are the axes, using a method of defining a 3D lookup table in which the brightness value as the mixing result is defined. Also works.

In addition, a 3D lookup in which a brightness value is defined as the gradation characteristic synthesized by mixing the color gradation characteristics and the monochrome gradation characteristics at the blending ratio W based on the saturation value c, with R, G, and B as the axis of the input gradation value. You can also use the method of defining the table.

In addition, instead of using a lookup table, an input gradation value may be outputted as a synthesized gradation characteristic by mixing the color gradation characteristic and the monochrome gradation characteristic based on the saturation value c by using an arithmetic expression.

Further, in the above embodiment, the value (brightness value) of the monochrome lookup table L1 and the value (brightness value) of the color lookup table L2 are mixed for each pixel based on the blending ratio W, but the input gradation of the input pixel By calculating a correction coefficient based on the blending ratio W to the value (or by performing the same processing with a lookup table), the color tone characteristic and the monochrome tone characteristic are mixed with the blending ratio W based on the saturation value c, and the brightness by the synthesized tone characteristic You may decide the value.

In addition, in the above embodiment, an example of performing gradation characteristic correction to a brightness value that satisfies γ2.2 curve with respect to gradation characteristic correction of color pixels, is not limited to γ2.2 curve, for example, gamma value May use a value of 1.8 to 2.6, and Rec. 709, PQ method (Perceptual Quantization), HLG method (Hybrid Log Gamma), etc. may be used as a brightness value that satisfies the grayscale characteristic.

In addition, the present invention is an image processing program for causing a computer to function as an image processing apparatus including a saturation value acquisition unit and a correction unit, wherein the saturation value acquisition unit provides the saturation value of the target pixel or the target pixel and its surroundings. An acquisition step of acquiring a saturation value of a target small region including a pixel, and a corrected gradation characteristic obtained by correcting the target pixel by the correction unit, based on the acquired saturation value, a color gradation characteristic and a monochrome gradation A step of correcting the target pixel so as to match the synthesized gradation characteristics by mixing characteristics at a predetermined mixing ratio, and if the saturation value is c and the mixing ratio of the color gradation characteristics is W, c is a variable The value of W is represented by the relationship W=f(c), and can also be realized as an image processing program that satisfies the above conditions.

Further, the present invention can also be implemented as a computer-readable non-transitory recording medium storing the above-described program.

Although various embodiments according to the present invention have been described, these have been presented as examples and are not intended to limit the scope of the invention. This new embodiment can be implemented in various other forms, and various omissions, substitutions, and changes can be made without departing from the gist of the invention. The embodiment and its modifications are included in the scope and summary of the invention, and are included in the invention described in the claims and its equivalent range.

1: display control unit
2: memory
3: control panel
4: display
5: backlight
6: Communication Department
7: bus
11: Judgment
12: saturation value acquisition unit
13: mixing section
20: correction unit
21: mixing section
22: monochrome correction unit
23: color correction unit
100: image processing device
K: mix ratio table
L: lookup table

Claims (9)

An image processing apparatus comprising a saturation value acquisition unit and a correction unit,
The saturation value acquisition unit acquires a saturation value of a target pixel or a saturation value of a target small region including the target pixel and surrounding pixels,
The correction unit corrects the target pixel so that the corrected gradation characteristic obtained by correcting the target pixel matches the gradation characteristic synthesized by mixing the color gradation characteristic and the monochrome gradation characteristic at a predetermined mixing ratio based on the saturation value. and,
If the saturation value is c and the blending ratio of the color gradation characteristics is W, the value of W when c is a variable is expressed by the relationship W=f(c), and image processing satisfying the following conditions Device.
Condition: If the relationship in which the blending ratio W increases proportionally with respect to the saturation value c is W=g(c), when the saturation value is greater than or equal to the threshold value,
f(c)>αg(c)
There is a saturation value c and a multiplier α for satisfying α, and α≥1. The method of claim 1,
The image processing apparatus, wherein the correction unit includes a mixing unit that determines a mixing ratio of a color gradation characteristic for a color pixel and a monochrome gradation characteristic for a monochrome pixel based on the acquired saturation value. The method according to claim 1 or 2,
The relationship f(c) is
Relationship W1=f1(c) below the above threshold,
Including the relationship W2 = f2 (c) above the threshold,
If an arbitrary saturation value below the threshold is c1, and an arbitrary saturation value above the threshold is c2,
The image processing apparatus in which f1(c1)≦f2(c2) is satisfied. The method of claim 3,
The image processing apparatus, wherein the relationship f1(c) below the threshold is a proportional function. The method according to claim 3 or 4,
There is a second threshold when the above threshold is the first threshold,
The second threshold is equal to or greater than the first threshold,
When the saturation value is equal to or greater than a second threshold, the slope of the relationship f2(c) decreases toward zero. The method according to claim 1 or 2,
The relationship f(c) is at least a part of a sigmoid function. The method according to any one of claims 1 to 6,
The correction unit further determines the blending ratio W using a relationship in which the threshold value is set larger as the difference between the brightness value in the color gradation characteristic of the target pixel and the brightness value in the monochrome gradation characteristic of the target pixel is larger. The image processing apparatus which performs correction by doing. As an image processing method,
An acquisition step of acquiring the saturation value of the target pixel or the saturation value of the target small region including the target pixel and surrounding pixels;
A correction step of correcting the target pixel such that the corrected gradation characteristic obtained by correcting the target pixel matches the gradation characteristic synthesized by mixing the color gradation characteristic and the monochrome gradation characteristic at a predetermined mixing ratio based on the saturation value Including,
If the saturation value is c and the blending ratio of the color gradation characteristics is W, the value of W when c is a variable is represented by the relationship W=f(c), and the following conditions are satisfied. Way.
Condition: As the saturation value increases from the minimum value to the maximum value, when the relationship in which the mixing ratio increases proportionally from the minimum value to the maximum value is W=g(c), when the saturation value is greater than or equal to the threshold value,
f(c)>αg(c)
There is a saturation value c and a multiplier α for satisfying α, and α≥1. An image processing program for causing a computer to function as an image processing apparatus having a saturation value acquisition unit and a correction unit,
An acquisition step of acquiring, by the saturation value acquisition unit, a saturation value of a target pixel or a saturation value of a target small region including the target pixel and surrounding pixels;
The corrected gradation characteristic obtained by correcting the target pixel by the correction unit coincides with the gradation characteristic synthesized by mixing the color gradation characteristic and the monochrome gradation characteristic at a predetermined mixing ratio based on the saturation value. Let the computer execute the step of correcting the pixels,
When the saturation value is c and the blending ratio of the color gradation characteristics is W, the value of W when c is a variable is represented by the relationship W=f(c), and the following conditions are satisfied. program.
Condition: As the saturation value increases from the minimum value to the maximum value, when the relationship in which the mixing ratio increases proportionally from the minimum value to the maximum value is W=g(c), when the saturation value is greater than or equal to the threshold value,
f(c)>αg(c)
There is a saturation value c and a multiplier α for satisfying α, and α≥1.

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